linux-kernel - Re: [PATCHv4 bpf-next 2/6] uprobe: Do not emulate/sstep original instruction when ip is changed

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Message-ID: <aNPGqZfbViOaX82C@krava>
Date: Wed, 24 Sep 2025 12:23:37 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
	Andrii Nakryiko <andrii.nakryiko@...il.com>,
	Ingo Molnar <mingo@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>, bpf <bpf@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-trace-kernel <linux-trace-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Song Liu <songliubraving@...com>,
	Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	Hao Luo <haoluo@...gle.com>, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCHv4 bpf-next 2/6] uprobe: Do not emulate/sstep original
 instruction when ip is changed

On Wed, Sep 24, 2025 at 11:47:42AM +0200, Alexei Starovoitov wrote:
> On Wed, Sep 24, 2025 at 11:15 AM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > On Tue, Sep 16, 2025 at 03:28:52PM -0700, Andrii Nakryiko wrote:
> > > On Tue, Sep 16, 2025 at 2:53 PM Jiri Olsa <jolsa@...nel.org> wrote:
> > > >
> > > > If uprobe handler changes instruction pointer we still execute single
> > > > step) or emulate the original instruction and increment the (new) ip
> > > > with its length.
> > > >
> > > > This makes the new instruction pointer bogus and application will
> > > > likely crash on illegal instruction execution.
> > > >
> > > > If user decided to take execution elsewhere, it makes little sense
> > > > to execute the original instruction, so let's skip it.
> > > >
> > > > Acked-by: Oleg Nesterov <oleg@...hat.com>
> > > > Acked-by: Andrii Nakryiko <andrii@...nel.org>
> > > > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > > > ---
> > > >  kernel/events/uprobes.c | 7 +++++++
> > > >  1 file changed, 7 insertions(+)
> > > >
> > > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> > > > index 7ca1940607bd..2b32c32bcb77 100644
> > > > --- a/kernel/events/uprobes.c
> > > > +++ b/kernel/events/uprobes.c
> > > > @@ -2741,6 +2741,13 @@ static void handle_swbp(struct pt_regs *regs)
> > > >
> > > >         handler_chain(uprobe, regs);
> > > >
> > > > +       /*
> > > > +        * If user decided to take execution elsewhere, it makes little sense
> > > > +        * to execute the original instruction, so let's skip it.
> > > > +        */
> > > > +       if (instruction_pointer(regs) != bp_vaddr)
> > > > +               goto out;
> > > > +
> > >
> > > Peter, Ingo,
> > >
> > > Are you guys ok with us routing this through the bpf-next tree? We'll
> > > have a tiny conflict because in perf/core branch there is
> > > arch_uprobe_optimize() call added after handler_chain(), so git merge
> > > will be a bit confused, probably. But it should be trivially
> > > resolvable.
> >
> > Nah, I suppose that'll be fine. Thanks!
> 
> Thanks! Applied.
> 
> Jiri,
> in the future, please keep the whole history in the cover letter.
> v1->v2, v2->v3. Just v4 changes are nice, but pls copy paste
> previous cover letters and expand them.

ok

> Also please always include links to previous versions in the cover.
> Search on lore sucks. Links in the cover are a much better
> way to preserve the history.

will add them in future, thanks

jirka